What are the pros and cons of using a flags enum?

问题:

I'm receiving several bit fields from hardware.

My code was originally:

public readonly byte LowByte;

public bool Timer { get { return (LowByte & 1) == 1; } }

Then I remembered the flags enum and am considering changing it to:

[Flags]
public enum LowByteReasonValues : byte
{
    Timer = 1,
    DistanceTravelledExceeded = 2,
    Polled = 4,
    GeofenceEvent = 8,
    PanicSwitchActivated = 16,
    ExternalInputEvent = 32,
    JourneyStart = 64,
    JourneyStop = 128
}

public readonly LowByteReasonValues LowByte;

public bool Timer { get { return (LowByte & LowByteReasonValues.Timer) == LowByteReasonValues.Timer; } }

and so on.

Which is best practice and what if any are the pros and cons of each approach?

EDIT: I'm interested to know if there are any practical differences between the two approaches, particularly in regards to performance. I'm not wishing to solicit opinion on coding styles (unless it comes from Microsoft guidelines) as that would see the question closed as unconstructive. Thanks.

回答1:

At the very least, your second example has better semantics and indicates the meaning of the bits within the code. There is some documentation within the code of what the bit is used for.

Otherwise, based on your first example, you will need to add comments since you are basically twiddling magic (bit) numbers, which makes the code much more difficult to read, especially by another person not familiar with it. Even if you yourself will be maintaining this code six months down the road, you may find it difficult to remember what bit 5 was used for.

回答2:

The later is best practice since it makes your code more readable

回答3:

If you are using .NET 4.0, you can now use the HasFlag method to check whether an enum contains a specific bit. This makes it even more readable than the previous method of checking.

[Flags]
public enum LowByteReasonValues : byte
{
    Timer = 1,
    DistanceTravelledExceeded = 2,
    Polled = 4,
    GeofenceEvent = 8,
    PanicSwitchActivated = 16,
    ExternalInputEvent = 32,
    JourneyStart = 64,
    JourneyStop = 128
}

public readonly LowByteReasonValues LowByte;

public bool Timer 
{
  get 
  { 
    return (LowByte.HasFlag(LowByte.Timer));
  } 
}

More information on MSDN.